Load-supporting device

ABSTRACT

A load-supporting device comprising at least one air cushion lifting pad in combination with a compliant ground-effect surface provided by elastomeric material, and means for supplying pressurized fluid to each pad to form a fluid cushion between each pad and the compliant surface.

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority John Kerr Cambuslang, Glasgow,Scotland; lan Lasbrey, Beliast, Northern Ireland 802,840

Feb. 27, 1969 Oct. 19, 197 1 National Research Development CorporationLondon, England Mar. 2, 1968 Great Britain LOAD-SUPPORTING DEVICE 9Claims, 10 Drawing Figs.

US. Cl......

Int. Cl. Field of Search 125, ll6;'214/1 AB; 94/7;244l1 14'"nun"sun-"nu".

180/125, 94/7, 104/23 FS 360v l/00 References Cited UNITED STATESPATENTS 8/1932 Allaro 94/7 UX 5/1958 Seck 180/116UX 7/1961 Kelly2l4/1ABX 9/1963 Macks 180/125 X 2/1966 Cockerell 180/124 12/1968Nagamatsu. 180/124 2/1962 Cousino et al. 94/7 11/1959 Simmons 244/114 X7/1966 Bertin 180/116 X 5/1970 Crowley 180/124 Primary Examiner-A. HarryLevy Attorney-Cameron, Kerkam & Sutton ABSTRACT: A load-supportingdevice comprising at least one air cushion lifting pad in combinationwith a compliant ground-effect surface provided by elastomeric material,and means for supplying pressurized fluidto each pad to form a fluidcushion between each pad and the compliant surface.

PATENTEDUCT 19 I97! SHEET 3 [1F 3 LOAD-SUPPORTING DEVICE This inventionrelates to a load-supporting device.

It is known to use small air cushions both of the plenum chamber typeand the air curtain contained type, on such devices. It has also beenproposed to use a pad of porous material as an air-cushion device. Suchdevices are limited in the load they can support. If Ws is the specificload and Pr is the supply pressure, then Ws/Ps, for a normal groundsurface, is not usually higher than 0.2 to 0.4.

It has now been found that if an air cushion is used with a compliantsurface, then a very much higher ratio of Ws/Ps can be obtained, and ifa porous air-cushion pad is employed, then the ratio is higher than canbe obtained with plenum chambers. Air curtain contained cushions operateat very low specific loads, for example Ws p.s.i., compared with thesesystems.

Accordingly, the present invention provides a load-supporting devicewhich comprises a fluid-cushion lifting pad in combination with acompliant surface, the device including means to supply fluid,preferably air under pressure, to the lifting pad, so that a cushion ofair or a thin layer of air is formed between the under surface of thepad and the compliant surface.

Preferably the lifting pad is of the porous pad type rather than an openplenum chamber or air-curtain type.

Preferably the device includes a number of separate porous pads ordiscs. The pads or discs may, for example, be supported at the ends ofresilient legs, or they may be supported individually by springs. Thesprings may be mechanical or they may be pneumatic or hydraulic.

The porous material may, for example, be sintered metal, compacted intoa disc, such as sintered stainless steel or brass.

Materials which are sufficiently compliant for the purposes of theinvention can be found among elastomeric materials such as syntheticrubbers, of which Neoprene (registered trade mark) is a particularlysuitable example, silicone rubbers, and so on, including nonrubber-basedmaterials. Materials used satisfactorily with an air bearing accordingto the invention have had a hardness between 30 and 90 shore hardnessand preferably between 50 and 60.

The degree of compliancy has been found to depend on the appliedspecific loading, and this is also related'to the shear modulus. Inpractice the ratio of specific load to shear modulus should lie in therange 0.05 to 1.0 or, more generally speaking, the specific load inpounds per square inch should be equal to the shear modulus in the sameunits, as a first approximation in choosing a compliant material.

The choice of a suitable compliant surface enables Ws/Ps ratios as highas 1.0 to be obtained but in practice the ratio will usually be in therange 0.5 to 0.85.

One advantage of using this type of supporting device with a compliantsurface is that the porous pads will travel over small gaps betweenadjacent section of the compliant surface.

Use of sheets of the compliant material enable heavy loads to be movedacross ground which would otherwise be too uneven, or too hard, toprovide the necessary combination of compliance and smoothness tosupport the load with reasonably economical use of power.

Where the material is laid over a particularly rough floor the compliantmaterial, say in quarter-inch-thick sheets, may be laid over a thinsheet of a stiffer material such as plastic or metal, in turn laid on asoft material such as foamed rubber or other foamed material. The thinmetal spreads the load.

While use of the invention will normally be such that the pad movesrelative to a stationary compliant surface, this is not necessarily thecase. Movement of the surface relative to the pad would be relevant toapplication in a conveyor system, for example, with a web having acompliant surface movable over and around a sequence of pads. Similarly,a load-carrying pallet having a compliant undersurface can be moved overa floor fitted with a regular array of lifting pads.

Also it might be noted that while it will be found convenient in manycases to locate the relevant source of pressurized fluid for movementwith the pad or pads the latter can be arranged for movement relative toa fixed source to which they are connected by way of a flexible air lineor the like.

In any event, for a clearer understanding of the practical applicationof the invention, reference will now be made, by way of example, to theaccompanying drawings in which:

FIG. I shows an industrial pallet incorporating the invention;

FIG. 2 is an enlarged section through one of the porous pads employedinboth FIGS. 1 and 3;

FIG. 3 shows a cradle for transporting a gas turbine engine, the cradleembodying the invention;

FIG. 4 shows a television camera modified in accordance with the presentinvention;

FIG. 5 shows one of the porous supporting pads used at the lower ends ofthe legs of the television camera;

FIG. 6 shows a tracked hovercraft in which the track and the hovercraftare modified to embody the invention;

FIG. 7 shows, in section, an alternative form of load-supportingcompliant surface for use with the invention;

FIG. 8 is a side view of a trolley-type pallet embodying the invention;

FIG. 9 is a sectional view of the pallet shown in FIG. 8, taken on theline IX-IX in the latter figure; and

FIG. 10 is a plan view of the pallet shown in FIG. 8.

In FIG. 1 is shown a pallet 10 which is supported at its four corners bylegs ill. At the lower end of each leg is an aircushion pad 12 suppliedwith air from a bottle 13 controlled by a valve 14. The air is suppliedto each of the four pads 12 through flexible pipes 15 and the palletrests on a compliant surface made of quarter-inch-thick Neoprenesheeting 16.

The form of each of the pads is shown in FIG. 2. Each pad 12 consists ofa housing 17 to which the pipe 15 is attached so that air can besupplied through passage 18 to an annular chamber 17a within thehousing. The lower end of the pad 12 is closed by a thin disc 19 ofsintered stainless steel and the outer edge of the housing 17 is peenedover at 20 to seal the edge and to make a smooth rounded edge to thepad. Added support for the disc 19 is provided by a central lug 21 towhich the disc is held by a screw 22. In addition the disc is attachedto the adjacent inner surfaces of the housing, such as 23, by Araldite"(registered trademark). Air passes through the pipe 15 via passage 18 tothe annular chamber and then through porous sintered metal disc 19 toform an air layer 24 between the lower face of the disc and thecompliant surface of the sheet 16.

In FIG. 3 the invention is shown applied to a lifting and transportingcradle for a jet engine 25. The engine rests on the cradle 26 which hasfour legs 27 terminating in respective feet 28 from each of which extendsix resilient fingers 29, and at the end of each of which fingers is apad 30. Each of the pads 30 is similar in construction to the one shownin section in FIG. 2, while each of the fingers 29 may be similar inconstruction to the pad-supporting means shown in FIG. 5.

The air supply for the pads is provided by a bottle 31 and controlled bya valve 32, the air passing through pipes 33 to each of the sets of pads30.

Again, in use, the cradle is moved across a compliant surface such as 16in FIG. I. The compliant material can be laid permanently or it can beput down in strips as required.

In FIG. 4 is shown a television camera 34 which has tripod legs 35terminating in support pads 36 resting on a compliant surface 37 formedof sheets of silicone rubber. As will be apparent from the drawing, thegaps between adjacent sections of the compliant surface 37 are small inrelation to the dimensions of the pads 36.

Each of the pads 36 is of the form shown in FIG. 5 and is supported atthe end of the leg 35 by means of a spring 38 and a flexible casing 38atherearound. The casing 38a is airtight so that air passing down througha passage 39 in the leg 35 will enter a further passage 40 leading to anannular chamber 41. The pad 36 is closed by a disc 42 of sintered brass.

This arrangement not only enables the camera 34 to be moved quickly andeasily across a television studio floor, but also results in extremelyquiet operation which is essential in such a studio, particularly if thestudio is laid with a continuous compliant surface with no joints.

In FIG. 6 the invention is shown as applied to a tracked ground-effectvehicle. The vehicle 43 is shown supported on a track 44. The ends ofthe track arms terminate in rectangular section members 45 carryingstrips 46, 47 and 48 of compliant material such as Neoprene."

The vehicle is supported by means of pads 50, 51 and 52, each pad beingof the form shown in FIG. 2. The pads 50 and 52 provide verticalmovements and the pads 51 restrain sideways movement.

There may be, say 25 pads 52 on each side of the craft and acorresponding number of pads 50 and 51, the pads being about inches indiameter.

This arrangement enables the track construction to be very cheapcompared with previous proposals, since the strips 48 etc. need only beabout a foot wide which means that the concrete rectangular sectionmembers 45 can be as little as a foot wide which reduces cost comparedwith the large and wide tracks proposed previously.

In FIG. 7 is shown an alternative form of compliant surface. A sheet 53of Neoprene" about a quarter-inch thick is laid on top of a sheet 54 ofnonporous, stiffer material, such as a thin metal sheet or plasticsheet, aluminum being a possible material. The aluminum sheet 54 restson a 3-inch-thick layer of foamed rubber 55, which in turn is laid onthe uneven ground 56.

With this arrangement the layer 53 provides the compliant surface, thealuminum sheet 54 spreads the load and the foamed rubber 55 smooths outunevenness in the ground surface.

ln FIGS. 8, 9 and 10 is shown an industrial-type pallet modified inaccordance with this invention.

The pallet is in the form of a trolley which has a platform 60 supportedthrough a number of bellows-type springs 61, each spring being attachedto a supporting device 62 in the form of a circular member carrying agroup of five symmetrically spaced porous pads 63, supplied from acommon air supply.

There are four groups of the porous pads spaced along the length of thetrolley. The air supply can be through a flexible airhose reel 65. Thetrolley has an end handle 66 for manual manipulation.

The trolley can either be used to support objects spaced on the platform60, or, for example, two trolleys can be used, one being positionedunder each end of a larger platform or any other large object which hasto be moved.

While in the above embodiments reference has been made to the use ofair, other gases and also liquids can be employed. In the case ofliquids there is an advantage that very much higher values of Ps can beobtained economically, for example values of several thousand p.s.i. Theuse of liquid will, though,

require use of compliant materials having correspondingly higher shearmodulus values, materials suitable for this purpose being textile orwire-reinforced elastomers, for example, such as are used in conveyorbelts, etc., preferably with substantially homogeneous reinforcement.

We claim:

1. A load-supporting system comprising at least one fluidcushion liftingpad in combination with a layer of compliant elastomeric materialproviding a ground-effect surface, the lifting pad including a housinghaving a fluid chamber therein, means for supplying fluid under pressureto said chamber, and a rigid porous member forming the outlet of saidchamber through which said fluid passes to form a fluid cushion betweenthe pad and the compliant surface, the ratio of the specific loadapplied to said compliant surface by said pad compared to the shearmodulus of the elastomeric material being in the range 0.05 to 1.0.

2. A system according to claim 1 wherein said porous member is made ofcompacted sintered metal.

3. A system according to claim 1 wherem the elastomeric material has ahardness in the range 30 to shore hardness.

4. A system according to claim 3 wherein said hardness is in the range50 to 60 shore hardness.

5. A system according to claim 1 wherein said compliant surface isformed of a plurality of sections of said elastomeric material laid overan existing surface with gaps between adjacent sections which are smallin relation to the dimensions of the lifting pad.

6. A system according to claim 1 wherein said compliant material fonns aground-efiect surface on a track for a tracked ground-effect vehicle.

7. A load-supporting system comprising at least one fluidcushion liftingpad in combination with a compliant laminated ground-covering structurecomprising a layer of elastomeric material providing a ground-effectsurface, said layer of elastomeric material overlaying a sheet of stifimaterial which, in turn, overlays a layer of resilient material softerand thicker than the layer of elastomeric material, and means forsupplying fluid under pressure to the pad so that a cushion of fluid isfonned between the pad the compliant surface.

8. A system according to claim 7 wherein said stiff material is metaland said resilient material is foamed rubber.

9. A load-transporting system comprising a load-carrying body, aplurality of lifting-pad housings having chambers therein closed attheir lower ends by respective porous members, resilient meansconnecting said pads to depend from said body, a layer of compliantelastomeric material providing a ground-effect surface for said pads,and means for supplying fluid under pressure to said chambers to form afluid cushion between each of said pads and said surface, the ratio ofthe specific load applied to said compliant surface by each of said padscompared to the shear modulus of the elastomeric material being in therange 0.05 to 1.0.

1. A load-supporting system comprising at least one fluidcushion liftingpad in combination with a layer of compliant elastomeric materialproviding a ground-effect surface, the lifting pad including a housinghaving a fluid chamber therein, means for supplying fluid under pressureto said chamber, and a rigid porous member forming the outlet of saidchamber through which said fluid passes to form a fluid cushion betweenthe pad and the compliant surface, the ratio of the specific loadapplied to said compliant surface by said pad compared to the shearmodulus of the elastomeric material being in the range 0.05 to 1.0.
 2. Asystem according to claim 1 wherein said porous member is made ofcompacted sintered metal.
 3. A system according to claim 1 wherein theelastomeric material has a hardness in the range 30* to 90* shorehardness.
 4. A system according to claim 3 wherein said hardness is inthe range 50* to 60* shore hardness.
 5. A system according to claim 1wherein said compliant surface is formed of a plurality of sections ofsaid elastomeric material laid over an existing surface with gapsbetween adjacent sections which are small in relation to the dimensionsof the lifting pad.
 6. A system according to claim 1 wherein saidcompliant material forms a ground-effect surface on a track for atracked ground-effect vehicle.
 7. A load-supporting system comprising atleast one fluid-cushion lifting pad in combination with a compliantlaminated ground-covering structure comprising a layer of elastomericmaterial providing a ground-effect surface, said layer of elastomericmaterial overlaying a sheet of stiff material which, in turn, overlays alayer of resilient material softer and thicker than the layer ofelastomeric material, and means for supplying fluid under pressure tothe pad so that a cushion of fluid is formed between the pad thecompliant surface.
 8. A system according to claim 7 wherein said stiffmaterial is metal and said resilient material is foamed rubber.
 9. Aload-transporting system comprising a load-carrying body, a plurality oflifting-pad housings having chambers therein closed at their lower endsby respective porous members, resilient means connecting said pads todepend from said body, a layer of compliant elastomeric materialproviding a ground-effect surface for said pads, and means for supplyingfluid under pressure to said chambers to form a fluid cushion betweeneach of said pads and said surface, the ratio of the specific loadapplied to said compliant surface by each of said pads compared to theshear modulus of the elastomeric material being in the range 0.05 to1.0.